The need for high-quality, high-speed computer printers and other types of output printers with changeable formats has been evidenced in recent years. Developments have proceeded with respect to ink jet technology to answer this need. Most developments in the field of ink jet have related to pressure deflected systems such as taught by Sweet U.S. Pat. No. 3,596,275, wherein a single stream of ink droplets are selectively charged and passed through a uniform deflection field to impact various locations on a recording medium in accordance with the charge of each droplet. Thus, by applying suitable charging signals to the droplets, a visible human-readable printed record may be formed on the recording surface. This type of system requires very precise control over the charge placed on each droplet due to various factors such as the tendancy of similarly charged droplets closely adjacent to one another to repel each other and therefore impact the recording medium at unintended locations. The circuitry required to accomplish this precise control appears to be relatively expensive, especially when duplicated for each jet of a multi-jet printer, which is required to attain truly high speeds.
Another type of ink jet printing has been developed which offers the potential of attaining high-speed, high-quality variable printing without requiring the expensive precision charging control electronic circuitry. This type of printing may be called the binary pressurized type and is shown in Sweet et al, U.S. Pat. No. 3,373,437. This type of system generates a plurality of jets in one or more rows, selectively charging drops with a single charge signal for deflection by a constant field to an ink drop gutter. The uncharged drops continue along the original jet stream path to impact a recording medium. The precision control over charging is not required inasmuch as charged drops impact the gutter and not the recording medium. In the absence of selective deflection, the major disadvantage of this type of ink jet printing has been that one nozzle orifice is required for each printing position across the entire dimension of the path to be printed in a single pass.
High quality printing requires additionally, however, that adjacent spots on the recording medium either adjoin or slightly overlap one another to form characters or images. Lines comprising a series of adjacent spots must appear to have a relatively smooth edge.
However, multi-orifice ink jet drop generation requires that the nozzles have sufficient structures to withstand the pressure of the pressurized ink. This dictates a minimum separation of the orifices. Further, each stream is selectively charged by a separate charge electrode, imposing an additional minimum orifice separation requirement in order to accommodate the charge electrodes.
Other technologies having similar spacing problems have illustrated various ways of arranging the print elements. For example, Murray, U.S. Pat. No. 2,556,550 illustrates that the print elements may be arranged in a long line extending diagonally entirely across a page, and illustrates that the print elements may be arranged in two parallel rows orthogonal to the paper-to-print-element motion and staggered laterally. Taylor, U.S. Pat. No. Re. 28,219, employs laterally staggered rows for binary multi-orifice ink jet. Each row of jet orifices includes charging electrodes, deflection plates and gutters for that row, resulting in a complex arrangement requiring precision alignment between rows. Any attempt to employ the diagonal line arrangement may simplify the ink jet head structure, but would result in the requirement of data buffer storage for an entire page of data and complex electronics.
Hence, an object of the present invention is to provide an ink jet head arrangement giving sufficiently close spot deposition with less complexity and less storage requirements.